The present invention generally relates to a compact safety knife suited for use in paper cutting, pencil sharpening and like handicraft work and, more particularly, to a handy safety knife of a type having a knife blade automatically concealable when not in use.
Various knives are well known and currently commerically available. So far as the capability of the knife blade being concealed within the holer is involved, there is well known a safety knife of a type which comprises an elongated holder having a guide groove of a cross section similar in shape to a substantially flattened figure "C", an elongated blade member inserted in the guide groove for movement in a direction lengthwise of the blade member, and a manipulatable member having a portion exposed outside the holder through an axially extending slit in the holder and another portion coupled to the blade member. In this conventional safety knife, by applying an external force to the manipulatable member in a direction lengthwise of the blade member, the blade member can be selectively projected from and retracted into the guide groove in the holder. While the continued application of the external force is required to maintain the blade member in a position projected outwards from the holder when in use, an elastic tongue is integrally formed with the other portion of the manipulatable member and is frictionally engaged to a wall defining the guide groove such that, when the blade member is retracted into the guide groove, it can be held in the retracted position.
The conventional safety knife of the above described construction is satisfactory in many respects, but it has some disadvantages. One of them is the possibility that, when the safety knife is accidentally shaken with the opening of the guide groove pointed outwards, the blade member in the retracted position will project outwards through the opening of the guide groove. Therefore, the user of the conventional safety knife is exposed to dangers when the blade member is exposed outside of the holder in the manner described above. Although increased friction between the elastic tongue and the wall defining the guide groove may avoid this possibility, this brings about the adverse effect of requiring the application of a correspondingly increased external force for moving the blade member between the projected and retracted positions.
Another disadvantage is that, since the blade member is constituted by a razor blade which is specially designed for use in shaving, not only is the conventional safety knife bulky in size, but it also does not have a very good appearance.
A further disadvantage is that, since the conventional safety knife including the holder is made of a metallic material, not only is the manufacture thereof complicated, but also it requires a relatively high manufacturing cost. Although synthetic resin can be used as a material for the holder, the life of the knife would be reduced or the magnitude of friction required to be developed between the elastic tongue and the wall defining the guide groove would be reduced, because of the frictional wear of that portion of the holder which is held in contact with the elastic tongue.